I think you might be creating unnecessary suffering over this labeling as "soulmates." No one would really agree what a "soulmate really is as there is no perfect relationship. This expectation of a perfect relationship only brings with it tremendous suffering as you're then bound to judge yourself and come up short every time.
A relationship changes many times over the years, and the best indicator for longevity is that the two of you are best friends. Sounds like you and your partner are on a good track. Consider what your relationship might look like if you dropped this pressure to be soulmates and considered your relationship as perfect just as it is, wobbles and all.
That being said, there certainly is magic to strengthen a relationship. I'd start with a honey jar - google "honey jar spell." I'd also start a relationship altar where you and your partner spend time in prayer/togetherness every day, put photos of you two, burn candles, invoke diety, etc. Best of luck!